In a microprocessor-based control, cost considerations often mandate the use of lower speed processors. A DC motor can be controlled by such a processor by providing the processor output to a pulse width modulation circuit that operates on the same duty cycle as the microprocessor, such as 100 Hz, wherein the mark:space ratio is proportional to the processor output. Given the mechanical time constant of a typical DC motor, 100 Hz, pulse width modulation is entirely adequate. With such a system there would be an attendant "hum" produced by the harmonics of the pulse width modulator. While in many applications the hum would not be objectionable, in the context of a motor speed control located atop an elevator cab, such as for a door opening/closing mechanism, the hum would be discernable, and actually objectionable, especially when the acoustical properties of an elevator cab are considered.